Conventionally, a headrest structure of the above-stated kind is disclosed for example in the Japanese Laid-Open Publication No. 2008-253335. According to such publication, as described therein, two stays of a headrest are inserted in two holders provided in a top portion of a seat back of the seat, respectively, wherein the two holders are each made of a hard synthetic resin material and also each have a head portion projecting upwardly from a surface of the top portion of the seat back, such head portion having, provided therein, a lock mechanism operable for adjustably locking and unlocking the stay of headrest in vertical direction to permit vertical adjustment of the headrest relative to the seat back. In the headrest, there is provided a mechanical unit for allowing the headrest itself to be moved in forward and rearward directions. A trim cover assembly forming a part of the headrest is formed in a bag-like three-dimensional configuration having an opened side, and in assembly of the headrest, when affixing the trim cover assembly with the headrest, such opened side of the trim cover assembly is folded and closed at a bottom side of the headrest.
In such structure of headrest, the trim cover assembly covers an entire body of the headrest and also covers the bottom side of the headrest. Therefore, even when the headrest is lowered to a lowest position to the extent that the bottom side thereof keenly contacts the top portion of the seat back, no objectionable noise is generated from therebetween by the virtue of an elastic and pliable property of the trim cover assembly. Further, when the headrest is set at such lowest position, a portion of the trim cover assembly which covers the bottom side of the headrest is actually in contact with the head portions respectively of the afore-said holders. In that case, even when subjected to vibrations of a vehicle or other externally applied forces, it is unlikely that an objectionable noise will be generated from between that portion of the trim cover assembly and the head portions of the holders, considering the elastic property of the trim cover assembly.